The present invention relates to a refrigeration system working on an ammonia refrigerating cycle and CO2 refrigerating cycle, a system for producing CO2 brine to be used therein, and a refrigerating unit using ammonia as a refrigerant and provided with the system for producing CO2 brine. Specifically, the present invention relates to an ammonia refrigerating cycle, a brine cooler for cooling and liquefying CO2 by utilizing the latent heat of vaporization of ammonia, an apparatus for producing CO2 brine to be used for a refrigeration system having a liquid pump in a supply line for supplying to a refrigeration load side the liquefied CO2 cooled and liquefied by said brine cooler, and an ammonia refrigerating unit provided with said brine producing apparatus.
Amid strong demand for preventing ozone layer destruction and global warming these days, it is imperative in the field of air conditioning and refrigeration not only to draw back from using CFCs from the viewpoint of preventing ozone layer destruction, but also to recover alternative compounds HFCs and to improve energy efficiency from the viewpoint of preventing global warming. To meet the demand, utilization of natural refrigerant such as ammonia, hydrocarbon, air, carbon dioxide, etc. is being considered, and ammonia is being used in many of large cooling/refrigerating equipment. The adoption of natural refrigerant also tends to be increasing in cooling/refrigerating equipment of small scale, such as a refrigerating storehouse, goods disposing rooms, and processing rooms, which are associated with said large cooling/refrigerating equipment.
However, as ammonia is toxic, a refrigerating cycle, in which an ammonia cycle and CO2 cycle are combined, and CO2 is used as a secondary refrigerant in a refrigeration load side, has been adopted in many of ice-making factories, refrigerating storehouses, and food refrigerating factories. A refrigeration system in which ammonia cycle and carbon dioxide cycle are combined is disclosed, for example, in Japanese patent No. 3458310. The system is composed as shown in FIG. 9(A). In the drawing, the ammonia cycle gaseous ammonia is first compressed by the compressor 104 and is cooled by cooling water or air to be liquefied when the ammonia gas passes through the condenser 105. The liquefied ammonia is expanded at the expansion valve 106, then evaporates in the cascade condenser 107 to be gasified. When evaporating, the ammonia receives heat from the carbon dioxide in the carbon dioxide cycle to liquefy the carbon dioxide. On the other hand, in the carbon dioxide cycle, the carbon dioxide cooled and liquefied in the cascade condenser 107 flows downward by its hydraulic head to pass through the flow adjusting valve 108 and enters the bottom feed type evaporator 109 to perform required cooling. The carbon dioxide heated and evaporated in the evaporator 109 returns again to the cascade condenser 107, thus the ammonia performs natural circulation.
In the system of the above-described prior art, the cascade condenser 107 is located at a position higher than that of the evaporator 108, for example, located on a rooftop. Accordingly, hydraulic head is produced between the cascade condenser 107 and the evaporator having a cooler fan 109a. The principle of this is explained with reference to FIG. 1(B) which is a pressure-enthalpy diagram. In the drawing, the broken line shows an ammonia refrigerating cycle using a compressor, and the solid line shows a CO2 cycle by natural circulation which is possible by composing such that there is a hydraulic head between the cascade condenser 107 and the bottom feed type evaporator 109.
However, the prior art includes a fundamental disadvantage in that the cascade condenser (which works as an evaporator in the ammonia cycle to cool carbon dioxide) must be located at a position higher than the position of the evaporator (refrigerating showcase, etc.) for performing required cooling in the CO2 cycle. Particularly, there may be a case that refrigerating showcases or freezer units are required to be installed at higher floors of high or middle-rise buildings at customers' convenience, and the system of the prior art absolutely cannot cope with such a case.
To deal with this, some of the systems provide a liquid pump 110 as shown in FIG. 9(B) in the carbon dioxide cycle to subserve the circulation of the carbon dioxide refrigerant to ensure more positive circulation. However, the liquid pump serves only as an auxiliary means and basically natural circulation for cooling carbon dioxide is generated by the hydraulic head between the condenser 107 and the evaporator 109 also in this prior art. That is, in the prior art, a pathway provided with the auxiliary pump is added parallel to the natural circulation route on condition that the natural circulation of CO2 is produced by the utilization of the hydraulic head. (Therefore, the pathway provided with the auxiliary pump should be parallel to the natural circulation route.)
Particularly, the prior art of FIG. 9(B) utilizes the liquid pump on condition that the hydraulic head is secured, that is, on condition that the cascade condenser (an evaporator for cooling carbon dioxide refrigerant) is located at a position higher than the position of the evaporator for performing cooling in the carbon dioxide cycle, and above-mentioned fundamental disadvantage is not solved also in this prior art system. In addition, it is difficult to apply this prior art when evaporators (refrigerating showcases, cooling apparatuses, etc.) are to be located on the ground floor and the first floor and accordingly the hydraulic head between the cascade condenser and each of the evaporator will be different to each other.
In the prior art systems, there is a restriction for providing a hydraulic head between the cascade condenser 107 and the evaporator 109 that natural circulation does not occur unless the evaporator is of a bottom feed type which means that the inlet of CO2 is located at the bottom of the evaporator and the outlet of CO2 is provided at the top thereof as shown in FIG. 9(A) and FIG. 9(B). However, in the bottom feed type condenser, liquid CO2 enters the cooling tube from the lower side evaporates in the cooling tube and flows upward while receiving heat, i.e. depriving heat of the air outside the cooling tube, and the evaporated gas flows upward in the cooling tube. So, in the cooling tube, the upper part is filled only with gaseous CO2 resulting in poor cooling effect and only lower part of the cooling tube is effectively cooled. Further, when a liquid header is provided at the inlet side, uniform distribution of CO2 in the cooling tube can not be realized. Actually, as can be seen in pressure-enthalpy diagram of FIG. 1(B), CO2 is recovered to the cascade condenser after liquid is CO2 perfectly evaporated.
A brine producing apparatus, which comprises an ammonia refrigerating cycle, a brine cooler for cooling and liquefying CO2 by utilizing the latent heat of vaporization of ammonia, and an apparatus for producing CO2 brine having a liquid pump in a supply line for supplying to a refrigeration load side the liquefied CO2 cooled and liquefied by said brine cooler, is generally unitized. Particularly in the ammonia cycle, the condensing section where gaseous ammonia compressed by the compressor is condensed to liquid ammonia is composed as an evaporation type condenser using water or air as a cooling medium.
The construction of the ammonia refrigerating unit comprising the evaporation type condenser is disclosed in Japanese Laid-Open Patent Application 2003-232583 which was applied for by the same applicant of the present invention. The construction of the ammonia refrigerating unit of this prior art is shown in FIG. 10. The refrigerating unit is composed such that; a lower construction body 56 integrating a compressor 1, a brine cooler 3, an expansion valve 23, a high-pressure liquid ammonia refrigerant receiver 25, etc. is of a hermetically sealed structure; an upper construction body 55 located on said lower construction body 56 is of a double-shelled structure integrating a water sprinkler head 61 of an evaporation type condenser and a condensing section in which a heat exchanger 60 is integrated; a cooling fan 63 sucks cooling air from an air inlet provided in an outer casing 65, the cooling air being introduced to the heat exchanger 60 from under the evaporation type condenser; the cooling air together with the sprinkled water cools the high-pressure, high-temperature ammonia gas flowing in inclined cooling tubes of the heat exchanger 60 to condense the ammonia, the sprinkled water rendering leaked ammonia harmless by dissolving the leaked ammonia.
The evaporation type condenser is composed of the inclined multitubular heat exchanger 60, water sprinkler head 61, eliminators 64, and cooling fan 63 which sends out the air after heat exchanging. The outer casing 65 is provided to surround the cuboidal condensing section, the section including the heat exchanger 60, water sprinkler head 61, and eliminators 64, and being open downward to allow cooling air to be introduced into the condensing section in order to form the double-shelled structure.
The inclined multitubular heat exchanger 60 is composed of a pair of tube end supporting plates each having headers 60c, 60d, and a plurality of inclined cooling tubes 60g. Water is sprinkled from the water sprinkler head 61 provided above the heat exchanger 60 to the inclined cooling tubes 60g to cool the pipes utilizing the latent heat of vaporization of water. The cooling air introduced from the air inlet passes through the eliminators 64 and is sent out by the cooling fan provided above the eliminators 64.
A plurality of eliminators 64 are juxtaposed on a plane to prevent water droplets scattered from the sprinkler head 61 toward the inclined cooling tubes 10g from flying. Therefore, pressure loss of the air flow when the air sucked by the cooling fan 63 passes through the spaces between the eliminators 64 is large, which makes it necessary to increase fanning power resulting in an increased noise and driving power. (Arrows in the drawing indicate air flows.)
Further, in the case where apparatuses working on ammonia and some of the apparatuses working on carbon dioxide are unitized and accommodated in the lower construction body as mentioned above, it may happen that ammonia leaks from the bearings, etc. of the compressor. Although the lower compartment is hermetically sealed, a counter measure to deal with ammonia leakage is necessary to be provided because ammonia gas is toxic and inflammable.